Wonderful - showing how little magic there really is in kernel programming. I recommend that everyone who does Linux programming go through this tutorial, even if just for fun - and for the sake of seeing how different the world on the other side of the syscall is. When writing a kernel-mode driver, a single bug usually means a reboot: either because you screwed up some refcount, so the module cannot be unloaded anymore - or because you clobbered something badly and the kernel is toast.

Having a driver-writing background, I silently laugh at the recent unit testing hype - I simply know from experience there are areas where you need much more care, gut and skill than def test_something(). And besides, you just can't unit-test a DMA transfer.